1. Field of the Invention
This invention relates to containers, especially metal cans, and more particularly to such containers that have a self contained means for opening by hand without requiring separate mechanical opening device. The containers may be used for almost any product, but they are most commonly used for liquids, and especially for carbonated beverages where they may be subjected to high internal pressures of 100 pounds per square inch or more. The contents may be poured out, or the user can drink directly from the can.
The invention applies to the types of containers which are commonly called easy-opening or self-opening containers. It applies particularly to the various types which have an opening area or segment which is defined by a score line in the top, and to one end of which a lifting tab is attached for first rupturing the score line at the tab end, and then for tearing the segment open by progressive rupturing along the score lines defining the borders of the segment. The segment is usually elongated and often wedge shaped, and usually extends from the rim to near the center of the top where the opening serves to admit air as the contents are discharged.
The opening device is generally located in the top of the can, and for this reason the top is usually made of aluminum because it may be made thicker than steel, and is much easier to score accurately. Aluminum is softer for easier rupturing along the score lines. Also the lifting tab, which is generally in the shape of a ring, is often attached to the segment end by an integral rivet drawn from the metal of the segment, providing an inexpensive and leakproof attachment. Prior art teaches several ways to construct the tab in such a way that a light pull on the tab will through leverage means exert a very high lifting force on the rivet, as required to initiate rupture in the small arc of score line adjacent the rivet. Some ring tabs initiate rupture further away from the rivet, but they must be larger and more expensive. A steel container top is also in use. It has an aluminum frame adhesively mounted in the top, and is fitted with an aluminum panel having a score defined removably segment. The tab is an extension of the metal of the panel, and a soft foamed plastisol seals around the tab base for easy rupture.
Beverage containers made with tear out segments are often opened outdoors, and because of their great popularity, the discarded tab and sharp edged segments have become a nuisance on the ground from appearance and safety standpoints, and when thrown in the ocean they endanger fish. Easy opening containers that have opening segments that do not remain attached to the can are being legislated against in some states.
My invention primarily concerns the field of use where the opening segment remains attached to the container, but some of the improvements of the invention apply also to tear out segments that are discarded separately, and of coarse at present this is by far the largest field.
2. Description of Prior Art
The type of easy opening top with a wedge shaped opening segment defined by a score line, and with a ring shaped lifting tab attached to one end has been very successful due to its low cost, ease of manufacture, freedom from leakage, resistance to damage during shipment, and ease of opening. The most common type has the ring attached by the integral rivet to the segment at the center of a round can, and arranged to tear toward the rim. Some have the ring attached near the rim and tear toward the center, but here the ring must be made stronger and is more expensive, and the pulling force to initiate rupture of the score at the rivet is generally greater.
Tests made on current production of the most common makes of openers with tear out segments and with the pull tab located at the center of the can top gave the following results. The initial pull to raise the tab ring and start the end score break is 2 to 4 pounds. The progressive pull required to tear the remainder of the side score lines up to the far end is 4 to 7 pounds. When the end score is reached the segment stands vertically, and the straight pull to break off the narrow width of score across the end varies from 8 to 12 pounds. The user often has to rock the segment back and forth to make the end rupture more easily than with a straight pull. This condition is taken care of by features of my invention.
There have been a number of methods proposed for attaching the opening segment to the container after it is torn out. One type of proposed tear strip opener has the tear strip in the form of a U with the pull tab attached at the closed end and located near the rim of the top. The score line extends across the end around the integral rivet holding the tab, and then down each side toward the interior to the far end of the segment where the metal remains unscored between the two side scores to serve as an attachment to the top after opening. U.S. patents based on this principle include Smith 3,327,891, Arfert 3,404,800, Luviano 3,441,168, Nicholson, 3,442,416, and Stolle 3,462,042.
When such a tear strip is torn along its length, the pull is upward or forward, and this imparts a continuous curvature to the metal of the tear strip. The strip can not be drawn out flat as the metal is resilient and will spring back, so the tear strip in this case will have an upward curvature, and it will also spring substantially away from the rim of the can on the far side. It can only be flattened down by hand, with the user may not do. As a result the sharp edged strip projects out to interfere with the drinker's nose, possibly causing cuts. Another disadvantage is that the metal takes a very sharp bend at the inner end where the score lines terminate, and this bend is almost 180.degree.. If the segment is bent back after use to its former position it will generally break off. The user may often do this, and if the resulting detached strip is thrown on the ground it will be sharper and more of a nuisance than the regular unattached segment.
U.S. Pat. No. Chun 3,420,398 provides an elongated wire or plastic strip positioned inside the can and connecting the under side of the top with the under side of a standard type of tear out segment like a tether. It is felt that having the attachment in the drink may be a disadvantage, and also the segment and ring tab at the end of the connector has an uncontrolled position after bending back, and may fall on the user's face. The considerable length adds to the cost if a plastic strip is used. A wire would have to be steel to hold on rivets, and this requires rust prevention at considerable cost.
It is thus seen that there remains a need for an improved method of attachment for the opening segment which will be low in cost, not interfere with drinking from the can, and not subject the user to possible injury.